METHOD FOR REDUCING POLLUTANT EMISSIONS AND CONSUMPTION OF AN ENGINE

摘要

A generally accepted and appropriate means to reduce pollutant emissions and consumption of passenger cars diesel engines is to apply multiple injection strategies. Assuming constant cylinder and bowl geometry and constant rail pressure the variation of the number of injections, injection quantity of each injection and separation between two consecutive injections are the major parameters which have to be optimised in order to fulfil both, the legislative emission limits and consumer requirements. A second, distinct approach to decrease pollutant emissions is to apply a single injection with a shaped injection rate. Ideally, rate shaping is achieved by a rise in injection pressure during one injection event, equal to that observed in cam controlled injection systems (e.g. Unit Injectors). For piezo driven common rail injection systems it might be possible to achieve similar effects by modifying the needle lift during an injection. The object of the present investigation is to compare and evaluate both methods in terms of pollutant emission, fuel consumption and robustness. For this purpose, experiments were carried out on single cylinder research engines. Multiple injection strategies with large hydraulic dwell times were compared with a short dwell setting simulating a "rate shaped" single injection. Rate shaping was implemented with a serial SIEMENS VDO piezo injector, performing multiple injections with hydraulic dwell times close to or equal zero.